It is well known that hard disk drives are susceptible to mechanical shock, particularly in a data access mode wherein a head arrangement is accessing a rotatable storage disk. Accordingly, dropping a hard disk drive, while it is engaged in a disk access, often produces a data loss or even a catastrophic failure of the drive. In this regard, a hard disk drive is generally substantially more resistant to mechanical shock when its head arrangement is in a parked position. One prior art approach, in attempting to avoid mechanical shock related failure during disk access, relies on moving the head arrangement to a parked position, if a mechanical shock event is anticipated. A specific example of this approach is presented in U.S. Pat. No. Re. 35,269, issued to Comerford.
The Comerford patent teaches a protective reflex system which utilizes a three axis accelerometer arrangement. Outputs derived from the three accelerometer axes are processed so as to identify a zero or reduced gravity state. The identification of such a state is useful in establishing the fact that the accelerometer arrangement may be falling. Of course, detection of a falling condition is predictive of an impending collision with the ground, such that preventive measures can, at least potentially, be taken prior to impact. In particular, it would be desirable to park the head or heads prior to a collision with the ground in order to avoid a catastrophic drive failure.
Comerford recognizes that the need to park the head arrangement may be urgent. In order to meet the need for urgency, the patent teaches the use of a dedicated processor in conjunction with the additional use of a central processing unit (CPU). The dedicated processor provides exclusive monitoring of the accelerometer arrangement. Responsive to detecting a value in a preset range of accelerations, the dedicated processor generates an interrupt to the CPU and parks the head arrangement. Apparently, the dedicated processor, like the CPU, is programmed for issuing standard commands to the hard disk, via a standard interface, since there is no specific teaching found in the patent with respect to a need for modification of the electrical interface of the hard disk. Unfortunately, it is submitted that a number of problems are associated with the approach taken by Comerford, as will be described in detail at one or more appropriate points below.
More recently, the use of a freefall sensing arrangement has been contemplated by Kionix, Inc. of Ithaca, New York in several papers. One paper is entitled USING THE KIONIX KXM52-1050 TRI-AXIS ACCELEROMETER FOR HARD DRIVE SHOCK PROTECTION, while another paper entitled INERTIAL SENSING FOR HARD DISK DRIVE DROP PROTECTION appeared in the online journal of the International Disk Drive Equipment and Materials Association in the second quarter of 2005. It is of interest that Comerford, at col. 4, lines 6-14 makes a recognition is shared by these papers. In particular, measurement of a freefall sensor output value, continuously over a period of time, suggests that a fall is in progress. The prior art of which Applicant is aware, however, fails to take the use of the freefall sensor output beyond this somewhat simplistic recognition. As will be described in detail below, there are further attributes of a freefall sensor output that are considered to be of interest.
Aside from freefall detection, Comerford and the prior art of which Applicant is aware, fails to recognize or account for certain additional environmental factors that can affect the operation of a hard disk drive in adverse ways. A number of these environmental factors are described in detail below and are considered to be significant with respect to protection of a hard disk drive in an anticipatory manner.
The foregoing examples of the related art and limitations related therewith are intended to be illustrative and not exclusive. Other limitations of the related art will become apparent to those of skill in the art upon a reading of the specification and a study of the drawings.